Practical JSON at the command line using Jello (Part 1)

[kellyjonbrazil]

A while back I wrote an article on my blog on ways to use jc and jq instead of sed, awk, grep, etc. to extract the data you want from command output. I thought I would post those same examples of filtering the JSON converted data from the rpm command using jello this time.

List the package objects that use the MIT license

Here is the method in jq:

$ rpm -qia | jc --rpm-qi | jq '.[] | select(.license == "MIT")'

And here is how you can do the same thing in jello:

$ rpm -qia | jc --rpm-qi | jello '[p for p in _ if p.license == "MIT"]'

[
  {
    "name": "ncurses-base",
    "version": "5.9",
    "release": "14.20130511.el7_4",
    "architecture": "noarch",
    "install_date": "Thu 15 Aug 2019 10:53:08 AM PDT",
    "group": "System Environment/Base",
    "size": 223432,
    "license": "MIT",
    "signature": "RSA/SHA256, Thu 07 Sep 2017 05:43:15 AM PDT, Key ID 24c6a8a7f4a80eb5",
    "source_rpm": "ncurses-5.9-14.20130511.el7_4.src.rpm",
    "build_date": "Wed 06 Sep 2017 03:08:29 PM PDT",
    "build_host": "c1bm.rdu2.centos.org",
    "relocations": "(not relocatable)",
    "packager": "CentOS BuildSystem <http://bugs.centos.org>",
    "vendor": "CentOS",
    "url": "http://invisible-island.net/ncurses/ncurses.html",
    "summary": "Descriptions of common terminals",
    "description": "This package contains descriptions of common terminals. Other terminal descriptions are included in the ncurses-term package.",
    "build_epoch": 1504735709,
    "build_epoch_utc": null
  },
  {
    "name": "ncurses-libs",
    "version": "5.9",
    "release": "14.20130511.el7_4",
    "architecture": "x86_64",
    "install_date": "Thu 15 Aug 2019 10:53:16 AM PDT",
    "group": "System Environment/Libraries",
    "size": 1028216,
    "license": "MIT",
    "signature": "RSA/SHA256, Thu 07 Sep 2017 05:43:31 AM PDT, Key ID 24c6a8a7f4a80eb5",
    "source_rpm": "ncurses-5.9-14.20130511.el7_4.src.rpm",
    "build_date": "Wed 06 Sep 2017 03:08:29 PM PDT",
    "build_host": "c1bm.rdu2.centos.org",
    "relocations": "(not relocatable)",
    "packager": "CentOS BuildSystem <http://bugs.centos.org>",
    "vendor": "CentOS",
    "url": "http://invisible-island.net/ncurses/ncurses.html",
    "summary": "Ncurses libraries",
    "description": "The curses library routines are a terminal-independent method of updating character screens with reasonable optimization.  The ncurses (new curses) library is a freely distributable replacement for the discontinued 4.4 BSD classic curses library. This package contains the ncurses libraries.",
    "build_epoch": 1504735709,
    "build_epoch_utc": null
  },
...
}

As you can see, we can use a simple list comprehension to get the same result.

Grab the name of the latest MIT licensed package

To grab the newest MIT licensed package installed we can use the following jq filter:

$ rpm -qia | jc --rpm-qi | jq 'sort_by(.build_epoch)[] | select(.license == "MIT")' | jq -sr '.[-1].name'

And here's how you do it in jello:

$ rpm -qia | jc --rpm-qi | jello 'sorted([p for p in _ if p.license == "MIT"], key=lambda x: x.build_epoch)[-1]["name"]'

"jc"

Oh look - it's jc! We could also do it this way using the operator module:

$ rpm -qia | jc --rpm-qi | jello '\
import operator
sorted([p for p in _ if p.license == "MIT"], key=operator.attrgetter("build_epoch"))[-1]["name"]'

"jc"

Finally, we can do it with a good old-fashioned loop:

$ rpm -qia | jc --rpm-qi | jello '\
plist = []
for package in _:
    if package.license == "MIT":
        plist.append(package)
result = sorted(plist, key=lambda x: x.build_epoch)
result[-1]["name"]'

"jc"

As you can see, there is more than one way to skin a cat in jello using the Python interpreter. That's it for this post. I'll add more examples in another. Do you have other ways to solve this problem in jello?